This invention relates to nuclear reactors and has particular relationship to the replacement of old split-pin assemblies of a guide tube of a nuclear reactor with new split-pin assemblies. According to the teachings of Calfo the old split-pin assembly, secured in the upper and lower counterbores of the lower circular flange of the lower guide tube (LGT) of the reactor, is processed in a pool of borated water in a work station which includes a plurality of robotic tools. Each guide tube is equipped with two split-pin assemblies located in the lower flange 180.degree. apart. The LGT is precisely positioned by a clamp-and-index tool. The old split-pin assembly is then severed by a metal-disintegration machine tool predominantly into two fragments; one fragment (herein referred to as the "nut fragment") consists of the residual part of the old nut and part of the old split pin threaded to it, and the other consists of the residual part of the split pin. The latter is extracted from the lower counterbore of the flange and deposited in a trash chute by a pin puller and expeller on the clamp-and-index tool. At this point it becomes necessary to remove the nut fragment from the upper counterbore of the flange and then to secure the new split-pin assembly in this flange. A difficulty which is imposed in carrying out this phase of the replacement is that the new nut is only partially accessible for mechanical processing. The nut extends from the upper counterbore into a slot in a wall of the LGT which has the shape of, and is referred to as, a "mousehole". Only a limited area external to the "mousehole" is accessible for removal of the nut fragment and for insertion in the upper counterbore of a new nut and threading it to a new pin. In addition, the tines (or leaves) of the pins must be properly aligned with respect to the top flange of the guide tube. This invention concerns itself with the phase of the overall replacement operation involving the securing of new split-pin assemblies.
It is an object of this invention to provide apparatus for securing the new split-pin assemblies in the flange without damage to the LGT after removal of the nut fragments from the upper counterbore of the flange, and, after the upper and lower counterbores have been cleaned.
The insertion of a new pin includes the proper alignment of the tines and proper torquing of the nuts to the pin.
The replacement is carried out in two stages. In the first stage the nut fragment is removed from the upper counterbore and is replaced by a new nut. This phase and the apparatus for carrying it out is described in parent U.S. Pat. No. 4,730,388. In the second stage to which the instant application is directed the new split-pin assembly is secured to the flange by threading and properly torquing a new nut onto a new split pin. The tooling and practice for this stage must meet the following conditions:
1. It must be capable of orienting the split pins in an LGT properly with respect to the top flange of the lower guide tube.
2. It must be capable of operation in the limited space external to the "mousehole".
3. It must be capable of operation in the space confines imposed by, and in cooperation with, the other tools at the robotic work station.
4. There must be accessibility for the supply of new split-pins from the deck above the pool.
5. The tooling and practice must be capable of automatic operation when coupled to a computer.
6. It must be capable of operating under borated water.
7. It must be capable of applying the proper torque to the nut.
It is an object of this invention to provide tooling which shall meet the above conditions for installing new splitpin assemblies in the lower flange of a LGT of a reactor without damage to the LGT.